1-Butene isomerization and metathesis over Mo/mordenite-alumina: Factors influencing product distribution and induction period

Effects of space velocity, reaction temperature and support acidity on product distribution and induction period in 1-butene isomerization and metathesis over Mo/mordenite-alumina were investigated. As revealed by the catalytic performance results, induction period and objective product were closely related to the reaction conditions. Lower space velocity led to longer induction period and higher propene yield. The optimal reaction temperature for propene production is around 150 ~C and it shifted to 100 ~C for ethene production. 1-Butene auto-metathesis predominated in the reaction network if the support with lower degree of sodium exchanged. And propene gradually became the dominant product upon increasing the support sodium exchange degree. 6Mo/H100Na0M-30A1 catalyst with a support of full sodium exchange degree exhibited the highest propene yield.

The Induction Period of Hydrate Formation in a Flow System

The appearance of turbidity due to large numbers of critical size hydrate nuclei may significantly affect the outgoing light intensity and the flow resistance in the pipe loop. The induction period of hydrate formation was determined by analyzing the experimental data——either based on the shading ratio data of laser detector or based on the pressure drop data of the flow system. The induction period of CC12F2 (R12) in pure water and that of CH4 in (tetrahydrofuran ＋ water) systems were then measured with the above two methods. Experimental data show that the induction period depends on the driving force exponentially. Flow rate also has a significant influence on the hydrate nucleation. A new induction period model taking the driving force and liquid flow rate into account was proposed. And it is successfully applied to the calculation of the induction period, which is in good agreement with the experimental data obtained in this study.

Fouling Induction Period of CaCO_3 on Heated Surface

Fouling induction period of CaCO3 on heated surface was studied with the micro video technology. The rates of nucleating and nuclei growing were measured under various experimental conditions. The experimental results showed that both nucleating and nuclei growing rates of CaCO3 increased obviously with surface temperature and concentration of reagents. In addition, the experiment of fouling induction period on the surface material of chemical plated nickel-phosphorus-polytetrafluoroethylene indicated that not only the nucleate rate of CaCO3 decreased but also some fouling particles with certain size were easy to peel off from the heated surface under shearing stress, which means that the property of surface material is one of the most important factors influencing fouling induction periods.

Investigating the Effect of Methylcyclopentadienyl Manganese Tricarbonyl on the Properties of Unleaded Motor Gasoline (1): Induction Period

In this paper, the effect of MMT on the induction period of unleaded motor gasoline was studied, the manganese concentration, storage period of MMT-blended gasoline and environmental variables such as temperature and radiation intensity were considered to be main factors affecting the induction period of gasoline,when MMT-blended gasoline was exposed to light. It is found from experiments that the addition of MMT can improve the induction period of gasoline that is shielded from light, and reduce the induction period remarkably,when the gasoline is exposed to light. However, the radiation intensity is proved to be the leading influencing factor among all the environmental variables investigated.

Methanol-to-olefin induction reaction over SAPO-34

The methanol-to-olefin induction reaction over the SAPO-34 was performed using a fluidized-bed system.We found that the whole induction period could be divided into three reaction stages.Further investigation of the reaction kinetics revealed that this induction reaction behavior was different from that over H-ZSM-5 catalyst.Compared with the H-ZSM-5,the generation of initial active centers is easier over SAPO-34 because of its limited diffusivity and the spatial confinement effect of the cages.However,the autocatalysis reaction stage is difficult over SAPO-34 because of the continuous formation of inactive methyladamantanes.

A molecular insight into coke formation process of vacuum residue in thermal cracking reaction

Understanding the coking behaviors has been considered to be really essential for developing better vacuum residue processing technologies.A battery of thermal cracking tests of typical vacuum residue at 410℃ with various reaction time were performed to evaluate the coke formation process.The total yields of ideal components including naphtha,atmospheric gas oil(AGO)and vacuum gas oil(VGO)of thermal cracking reactions increased from 10.89%to 40.81%,and the conversion ratios increased from8.05%to 43.33%with increasing the reaction time from 10 to 70 min.The asphaltene content increased from 12.14%to a maximum of 22.39%and then decreased,and this maximum of asphaltene content occurred at the end of the coking induction period.The asphaltenes during the coking induction period,at the end and after coking induction period of those tested thermal cracking reactions were characterized to disclose the structure changing rules for coke formation process,and the coke formation pathways were discussed to reveal the coke formation process at molecular level.

Catalytic performance of biological method seeds on jarosite process

The catalytic performance on jarosite process of jarosite seeds via biosynthesis and chemical processes were studied, respectively. The SEM and XRD results showed that biosynthetic jarosite seeds （BIO seeds） had smooth surface and mainly consisted of potassium jarosite. The chemical synthesis jarosite seeds （CHM seeds） had a loose cauliflower-like surface and mainly consisted of hydronium jarosite. The catalytic performance of BIO seeds was better than that of CHM seeds on the formation of final jarosite product. The induction time can be shortened to 20 min, the reaction temperature can be reduced to only 75 ℃, and the initial reaction speed was enhanced obviously, up to 3.933%/min. The crystallinity of final jarosite product using BIO seeds can achieve 97.22%, while it was only 12.89% without seeds. This indicates that the precipitation process of jarosite is more complete with BIO seeds.

Photolytic Model of Six Degradable Mulch Plastic Films

[Objective] This study aimed to solve the mulch plastic film pollution problems in Xinjiang, in order to provide reliable theoretical basis for the research on the degradation mechanism of biodegradable plastic films. [Method] The effect of illumination intensity on the decomposition of decomposable mulching films was investigated through simulating the field condition in laboratory. Regression analysis was employed to fit the processes of film decompositions. [Result] The weight loss ratios of different types of plastic films were closely related with the illumination. There was no sundry produced during the degradation process, but the weight was reduced, indicating that degradation produced gas, thus, ultraviolet rays had destructive effect on mulch plastic films. Different types of plastic films showed significant differences in the degradation speeds, and under the same conditions, the degradation speed of S4# with the induction period of 30 d was the fastest. With the extension of uv illumination time, the degradation became cumulative degradation process. [Conclusion] Under the uv rays, the weight loss ratio and illumination hours is regarded as a positive correlation relationship. The significant inspection shows that the data fitted degradation model can be described by the logistic model of Y = a/（1＋b×e -ct）, and all the parameters show significant differences （P0.01）.

Synergistic effect of combination of surfactant and oxide powder on enhancement of gas hydrates nucleation

In the present work we studied the induction periods of hydrate formation of natural gas in pure water, aqueous solutions of surfactants, and in the presence of surfactant together with aluminum oxide nanopowder, the activity of which as hydrate formation inducer was studied previously. Sodium dodecyl sulfate（SDS） or neonol AF-9-12 were used as the surfactants. It was demonstrated that the addition of either surfactants or aluminum oxide powder under our experimental conditions causes a decrease in the induction period of hydrate formation from;05 min for pure water to 30–35 min for water with additives. In the case of the simultaneous presence of surfactants and aluminum oxide powder in the system, induction period decreased to;0 min. So, the synergistic effect of the combination of surfactant and oxide powder on gas hydrate nucleation was demonstrated. Possible reasons of this effect have been discussed.

A viewpoint on catalytic origin of boron nitride in oxidative dehydrogenation of light alkanes

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides.Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes,negligible formation of CO2,and remarkable catalyst stability.From this viewpoint,recent works on boron nitride in the oxidative dehydrogenations of ethane,propane,butane,and ethylbenzene are reviewed,and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions.After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence,we conclude that pure boron nitride is catalytically inert,and an activation period is required under the reaction conditions;this process is accompanied by an oxygen functionalization at the edge of boron nitride;the B-O species themselves have no catalytic activity in C-H cleavage,and the B-OH groups,with the assistance of molecular oxygen,play the key role in triggering the oxidative dehydrogenation of propane;the dissociative adsorption of molecular oxygen is involved in the reaction process;and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy.A new redox reaction cycle based on the B-OH sites is also proposed.Furthermore,as this is a novel catalytic system,there is an urgent need to develop new methods to optimize the catalytic performances,clarify the catalytic function of boron species in the alkane ODH reactions,and disclose the reaction mechanism under realistic reaction conditions.

Studies on the Mechanism of Primary Nucleation of Ciprofloxacin Hydrochloride Monohydrate

A general expression for the relationship between induction periodand supersaturation was developed based on polynuclear approach.Different mechanism of primary nucleation in solution can beillustrated by the expression. The results of induction perioddetermined by laser scattering method shows that the crystallizationof ciprofloxacin hydrochloride monohydrate in water/ethanol oraqueous solution is by the mechanism of primary nucleation followedby one-dimensional diffusion growth, and then on-dimensionalcontinuous or 'birth and spread' growth on crystal face. The growthmechanism on the crystal face is affected by temperature and solvent.

Scaling and Removal of Calcium. Carbonate on Electroless Plating Surface

The scaling process of calcium carbonate on a low-energy heat transfer surface－electroless plating surface was investigated in a simulated cooling water system. Owing to the very low surface energy, the electroless plating surface exhibited less scaling susceptibility. A longer induction period and a lower scaling rate were obtained on the low-energy surface compared to copper surface under identical conditions. The calcite particles obtained on the electroless plating surface during the induction period were larger in size than those on copper surface because fewer crystals formed and grew at the same time on the low-energy surface. With increasing surface temperature, the induction period reduced and the scaling rate increased for the low-energy surface. When initial surface temperature was fixed, an increase in fluid velocity would reduce the induction period and increase the scaling rate due to the diffusion effect. However, when the heat flux was fixed, an increase in fluid velocity would decrease the surfacetemperature, and lead to a longer induction period and a lower scaling rate. The removal experiments of calcium carbonate scale indicated that during post induction period, the detachment was not obvious, while during the induction period, apparent removal of crystal particles was obtained on the electroless plating surface owing to the weak adhesion force. The more frequently the transient high hydrodynamic force acted, the more the detached crystal particles were.

Study on the Crystallization Mechanism of Spectinomycin Dihydrochloride

The growth mechanism of spectinomycin dihydrochloride crystal in pure water and acetone-water mixture at different temperatures has been studied by induction period measurement. The induction period was measured visually. The solid-liquid interfacial tension was determined on the basis of classical homogenous nucleation theory and the surface entropy factor was calculated. It was shown that the interfacial tension and surface entropy factor increased with the increase of acetone concentration and the decrease of temperature. It was demonstrated that the growth mechanism of spectinomycin dihydrochloride crystal was controlled by birth and spread growth in pure water or in acetone-water mixture at high temperatures and turned from birth and spread growth to spiral growth with the increase of acetone concentration in acetone-water mixture at low temperatures.

Kinetic Study on the Induced Coordination Reaction of Lanthanum with p-Acetylcarboxylazo

The absorption spectra of p-ACA(p-acetylcarboxylazo)and its complex with lanthanum ions were determined.The molar ratio of metal to ligand in the complex was estimated to be 1:2.An induction period was found existing in the coordination reaction between La and p-ACA and the effects of temperature,acidity and ionic strength on the induction period were studied.The reaction mechanism was depicted.The rate equation is consistent with the rate law,R=k[La(H_2O)_6^(3+)][H_3O^+],obtained by kinetic method.Finally the possible geometric structure of this complex was discussed.

Modern information technologies in construction of kinetic models for reactions of metal complex catalysis

For detailed study of complex chemical reactions mechanisms experiment is conducted for selected private reactions. This causes a problem of kinetic parameters getting--the same set of rate constants must describe both public and private reaction stages, and also a general mechanism. In this paper, solution of this problem for a reaction of olefins hydroalumination is proposed. To optimize the computational process a methodology of parallelization is elaborated. On the base of parallel computations, a kinetic model for the reaction assigned is constructed, and on its base, the physical and chemical conclusions about reaction mechanism are done.

STUDY ON MATHEMATICAL MODEL OF GAS EXPLOSION IN COAL MINE

Based on the principle of gas explosion in underground coal mine, mutation theory and mathematic method were adopted to establish" Mathematical model of coal mine gas explosion"and advanced some new concepts and ideas. The model can simply and precisely indicates underground air status and conforms to part of experimental data, provided a new method for research and experiment of explosion disaster theory.

Polymeric hollow fiber membrane for cooling crystallization seeding:On the mechanism of induced nucleation based on thermal transfer Author links open overlay panel

Cooling crystallization is an important separation process and particuology technology that requires accurate nucleation control strategies.Herein,we introduced the polymeric hollow fiber membrane with proper thermal properties as the effective nucleation induction interface during cooling crystallization.The heterogeneous nucleation control mechanism was introduced based on classical nucleation theory and the thermal transfer process.Interfacial properties and the thermal conductivity of two kinds of polymeric membranes,polytetrafluoroethylene(PTFE)and polyethersulfone(PES),were measured and simulated with the developed model.These two membranes possessed different nucleation induction periods,nucleation rates and crystallization performances,which validated that the hollow fiber membrane module could effectively accelerate the nucleation process compared to conventional cooling crystallization owing to the shorter nucleation induction period and the reduced solution surface tension.Due to the higher hydrophobicity and the lower roughness of the membrane surface,the PTFE membrane possessed a more moderate performance in generating stable heterogeneous nucleation than the one of PES membrane.Thus,the adjustable membrane property enabled the hollow fiber membrane-assisted cooling crystallization to possess the accurate nucleation control and desired terminal particle products.

Primary nucleation of lithium carbonate

A set of laser apparatus was used to explore the induction period and the primary nucleation of lithium carbonate.Results show that the induction period increases with the decrease of supersaturation,temperature and stirring speed.Through the classical theory of primary nucleation,many important properties involved in primary nucleation under different conditions were obtained quantitatively,including the interfacial tension between solid and liquid,contact angle,critical nucleus size,critical nuleation free energy etc.